Pull down on the sheet. Volume of air in the plastic cover. Internal air pressure down. The air moves from a high pressure from outside to inside. Inflatable balloons made out.
When you pull the rubber down. The volume of air in a plastic cover. Make the air pressure within the air-moving it from a prophecy that the high pressure from outside to inside, the balloons inflate out .
When you pull out the rubber down volume of air in plastic cover up, the pressure within the air-to-air, moving from a high pressure from outside to inside, balloon balloon